The Britannia was the first British n-gauge 4-6-2 model that
was produced by Minitrix for Hornby. It appears in the 1974 catalogue, but
is not listed as being a new model for that year. In 1979 when I first
started with N-Gauge, the price list shows
N203 for the grand price of £21.95, which would have been half my weekly salary
at the time. Not cheap then.

It is worth noting that there are two variants of the
Britannia produced by Minitrix. The early version is instantly recognisable
by its small, disc like front bogey wheels - unlike the later model shown in the photo above,
which has the larger spoked wheels which have become more familiar from the
A4 and A3 locos - which were not in production when the first Britannia came
out. The number used by Minitrix for the early Britannia was
51-2037-00, often abbreviated to
12037.

A new number for Britannia appeared on the tech sheets that are
included in every box - 51-2037-10. This new number also appeared in the
1981 catalogue from Minitrix - a change from the 1980 catalogue - but
confusingly failed to show an updated image, instead reproducing exactly the
same photo that had been in the 1980 catalogue ! I had always assumed that
the change of number married up with when the model was changed, but the tech
sheets still showed different part numbers for the front bogies and axles as the
original part numbers - which by 1981 could be seen as being different from the
spoked front bogies used by the Mallard that was introduced in 1980. In
which case, I don't know why the change of number.

There were significant changes to the later Britannia from the
earlier. The gearing is different, with cogs on the wheels being larger
than the original, and the idlers in between are smaller. The main cog
which interfaces with the worm gear had been black, and is now red - and again,
the number of teeth are different. The centre wheel has the square hole to
accommodate the square-pegged crank pin, the bogey wheels are different and the
base plate is plastic with moulded brakes. The valve gear had the new
plastic crank pin. In short, the new Mallard model arrived in 1980 and
some time after that the Britannia switched to using much of the same
components and chassis as the Mallard and Gresley. The later Boadicea, and
the two Scotsmen would also use the same chassis. The switch happened
sometime between 1981 and 1985, but I have no catalogues available to pinpoint
it. I cannot see a reason for changing the model number without changing
the model, so I am inclined to think it happened after Mallard was produced in
1980 and the stock of old Britannia components had been exhausted. I have
seen the Minitrix number for Boadicea as 51-2037-50, but this was subsequently
renumbered as 51-2042-00.